Electronic computing device



Oct- 14, 947- J. A. RAJCHMAN ELECTRONIC COMPUTING DEVICE Filed Nov. 25. 1943 3 Sheets-Sheet 1 w u. N 3.0%. Q

- attorney Oct. 14; 1947. J. A. RAJCHMAN.

ELECTRONIC COMPUTING DEVICE Filed Nov. 25, 1943 3 Sheets-Sheet 2 Gttomeg Oct. 14, 1947. J. A. RAJCHMAN ELECTRONIC COMPUTING DEVICE Filed Nov. 25, 194: 5 Sheets-Sheet s readily obtained in Patented Oct. 14, 1947 PATENT OFFICE 2,428,812 ELECTRONIC COMPUTING DEVICE Jan A.

of Delaware Rajchman, Princeton, N. Radio Corporation of America,

J., assignor to a corporation Application November 25, 1943, Serial No. 511,729

18 Claims.

This invention relates to computing devices of the electronic type, and has for its principal object the provision of an improved electronic computing device and method of operation whereby the product of two binary numbers is the form of potentials representative of the digits of such product.

All the computations are performed in terms of numbers. The present computing device is therefore of the numerical type, as contrasted with devices using continuously variable physical quantities, such as voltage, current or phase, as variable of computation. The whole computation is made in the binary system of numeration so that any number is expressed as a sum of powers of two in which the coefficients of the terms are zero or one. There are the only two digits of the binary system.

In this system, a number is expressed thus:

For any number the first digit from the right, or first "digital position, signifies whether there is a l=2 in the number or not, the second digital place whether there is a 2=2 or not, the third whethertthere is a 4:2 or not, the fourth whether there is an 8=2= or no e c.

It is obvious that fractions and fractional numbers can be expressed in the binary system in a manner similar to the decimal fractions by using a binal point analogous to the decimal point. A table of a few fractions would be:

For any number the first digit from the right of the decimal point signifies whether there is a w ether there is a V4=2' 2o no etc.

%=2' in the number or not, the second the third whether there is a 341 2- or This system of numeration was chosen because most electronic computations are more easily performed in it than in any other system. This unusual method of expressing numbers does not involve any practical difliculty so long as the input and output of the computing device are converted automatically to control some physical apparatus, such as an anti-aircraft fire control system. Under such conditions, no ciphering or deciphering to or from the decimal numeration is involved.

All the operations are made in a direct system in which the binary number is expressed by a system of as many potentials as there are digits in it, each potential having one of two definite values V1 and V2 corresponding respectively to the digits zero and one. All these potentials exist simultaneously on a system of conductors each carrying a potential corresponding to one digit of the number. Thus, for example, to express the first seventeen numbers five conductors would be required. The number 9 would be expressed by the following excitation of the five conductors: V1V2V1V1V2, since it can be written as 01001. In a computing device, two or more such systems of tensities are utilized though this could be accomplished in other ways. 1 be better understood from i the following description considered in connection I with the accompanying drawings and its scope is j indicated by the appended claims.

. of one modification granged, as shown in work whose intersections constitute the elements of a matrix corresponding to the terms AiBk. A

3 potentials are combined and a new system of potentials is derived from them. The result of the computation is the stationary final value of these output potentials and depends only on the stationary value of the input potentials, regardless of the manner in which they were reached. A sudden change in one or more input digits will, after short transients, cause the output potentials to reach their correct stationary values, so that the operation of the direct computing device may be considered as continuous. It does not involve any trigger elements with inherently stable states or any other "holding devices, nor does it necessitate any definite sequence, timing, or clearing pulses. Therefore, it is not a counter of any sort and does notinvolve impulses. It is basically the fastest type of numerical device, since no time is wasted in the proper sequencing of operations. 1

As pointed out above, the direct binarysystem of computation with fixed constraints, the output potentials or currents are in direct relation to the input potentials so that for each place or digit of the inputs and outputs there must be provided a conductor. 1

The product of two binary numbers a: and z! k: 2 =B,,2 +B,, ,2 +B.,=B,,2'=

where A1 and Br are equal to one or zero, can be written as:

In the product the coefi'lcients AiBk equal to zero or one, but are equal to if both A1 and Bk are equal to one. This property of the binary system of numeration in which the multiplication table of'the basic duces itself to a pure coincidence effect, is unique. In all other scales the number of answers in the basic multiplication table of digits is always greater than the radex. In accordance with this invention, that coincidence efiect is utilized to produce the terms AiBk. However, additions of infor the summations, al-

are also The invention will Referring to the figures of the drawing:

one only digits re- 1 Figure 1 is a diagrammatic illustration of the T Figure 2 is a wiring diagram of certain details of the device of Fig. 1, and Figure 3 is a similar diagram 01' another mod- 1 ification of the device of Fig. 1.

The two systems of potentials representing a: and z! are carried by two systems of wires ar- Fig. 1, in an orthogonal netvacuum tube 36 on each of these intersections is made to conduct only if there is coincidence of excitation of the two wires at such intersection, and therefore give a value to AiBk only-when A: and B1; are both one. All the coefiicients A113: corresponding to the power 2 are located on diagonal lines, horizontal on the Fig. 1. Thereconnections of a device for multiplying binary numbers,

v fore, if all the plate currents of the tubes on these ferent ways.

It has been found that the most convenient manner is as follows: Let

( i i+ i+i a+m will be obtained provided that the circuit of each carry-over tube, added to the circuits of the proper row, will contribute the same standard amount of current as the tubes of the matrix. This is so because any one of the coefiicients DHA multiplies the power 2 and is added precisely to the row corresponding to the (7'+A) power, as hereinafter explained in detail. To obtain the result, it suilices merely to provide anindicator on each of the (2p+2) rows which will be excited when the corresponding coeificient C is equal to one. The carry-over tubes 65 to 83 and indicator tubes 84 to 95 for the case of p=5 are shown on Fig. 1. The thirty-six tubes 36 of the matrix and the carry-over tubes 65 to 83 all contribute a standard current when conducting. The tubes 36 contribute no current when there is no excitation from one of the corresponding leads. Auxiliary amplifying tubes 96 to 3 are used in one modification or the invention.

The basic part of the multiplier is the circuit which will produce the'signals to excite the indicator and car -over tubes, according to Equation 4. This circuit is repeated on each one of the (2p+2) rows, with various degrees of complication because the maxima values which Sjmax can obtain are different for each row.

The range of numbers covered by the arrangement of Fig. 1 is five binary places in the multiplicand and five binary places in the multiplier, as indicated by the numerals under the 2: and y braces. The general mode of operation will be readily understood from a, few examples. There can, of course, be no carry-over from the tube 36 at the lower comer (diagonal No. l) of the orthogonal network because the current output from this tube can only represent one or zero. If it is one, the indicator 35, which may be a neon lamp or the like, so indicates' If it is zero, this lamp is not lit. 7

The second diagonal includes two tubes 36 and may, therefore contribute none, one or two units of current, depending on whether none, one or both tubes are simultaneously excited from the X-1, X-2, Y-l and Y-'2 leads. One carry-over tube 65 is therefore required to carry one to the and the total 2 each position tubes are excited from the leads z-l, a:2, :r-4, y 1, y-2, and zl-4. To this may be added one unit or current from the carry-over tube 65, making a possible total of four current units. One carry-over tube 66 is required to carry one to the next highest digital position when two or three tubes are excited and the total is 8 or 12 (1000 or 1100 in the binary system). Another carry-over tube 61 is required to carry one to the "16 digital position when four tubes are excited and the total is 16 (10,000 in the binary system).

The sixth diagonal includes six tubes 36 which may contribute as many as six units of current depending on whether one or more of the tubes are excited from the :1: and 11 leads. To this may be added the two units of the carry-over tubes 69 and I0, making a total of eight units of current. One carry-over tube I2 is required to carry one to the "64 digital position when two or three of the tubes are excited and the total is 64 or 96 (1,000,000 or 1,100,000 in the binary system). A second carry-over tube 13 is required to carry one to the 128 digital position when four, five, six or seven tubes are excited and the total is 128, 160, 192 or 224 (10,000,000, 10,100,000, 11,000,000 or 11,100,000 in the binary system). A third carry-over tube 14 is required to carry one to the 256 digital position when all eight tubes are excited and the total is 256 (100,000,000 in the binary system).

How the various matrix and carry-over tube are made to deliver the units of currents discussed above will be understood .upon consideration of Fig. 2, which shows a detailed wiring diagram of part of a modification which is similar to Fig. 1 as indicated by the use of the same reference numerals to indicate corresponding parts.

It will be observed that the tubes 36 of Fig. 2 are those of the sixth or longest diagonal of the matrix of Fig. 1, that at the intersection of the a: and y leads on this diagonal they are interconnected through resistors H5 (1,000,0009), and that the grids of the tubes 36 are connected to the midpoints of these resistors. The cathodes of the matrix tubes 36 and carry-over tubes 69 'are connected through resistors 116 (37,5009) to a source of 150 volts. The unexcited potential of the a: and y leads of the matrix is 350 volts and their excited potential is zero. It is apparent that any triode will conduct only when both driving wires are zero, and in that condition the current through the triode will be essentially determined by the 150 volts applied to the cathode resistance returns, and the value of this resistance, and will depend only slightly on the actual characteristic of the triode. The currents of all the S triodes located on the same row, that is corresponding to the same power of 2, are caused to flow through a common resistance 117 (3,2009). To each row of triodes corresponds a number M of amplifying pentodes H8, H9 and I20 and an indicator tube I2I equal to the number (m+1) of terms in Equation 4, expressing S as a binary number.

The method used to excite these tubes H8, H9 and I20 consists of coupling to each control grid, in addition to the potential of the common anodes, several additional potentials through an appropriate network of resistances I22 to I21 and I29 to I32. These additional potentials are those of cathodes of the carry-over tubes 12, I3 and 14, each of which is controlled by a corresponding amplifying-tube. The values of the resistors are 450,0000 for I22, 562,5000 for I23, 1,275,0000- for I24, 1,275,0009 for I25, 5625009 for I26, 450,000o

5 and I20 are coupled to the grids of the carryv for I21, 2,662,000!) for I29, 2562,5000 for I30, 562,- 5009 for I3I and 450,0000 for I32.

The grids of the indicator tube I2I and of the three amplifying tubes H8, H9 and I20 are all coupled to thebus I33 at the common potential of the plates of the intensity tubes 36, and are, in general, all coupled-through resistors I35 to I38 to the bus I34 maintained at a convenient negative potential. The values of these coupling resistors are 7739 for I35, 1385,0000 for, I36, 5,560,000!) for I31 and w for I38. In addition, each grid is connected to buses I39, I40 and I, but only to the busescorresponding to the carry over or a power of two greater than that corresponding to that particular amplifier tube. This tube I2I is coupled to I34, I39 to I and I33; I20 to I34, I40, I and I33; H9 to I34, I40 and I33, and H8 to I34 and I33. The values of the coupling resistances between these buses and the grids of the amplifying tubes are so chosen that when the first carry-over tube I2 is turned on (bus I39) it tends to vary the potentials of the grids to which it is coupled by an amount twice that which tends to be established by the standard variation of potential of the bus I33 or main driving potential, when the second carry-over tube 13 is turned on (bus I40) it tends to vary the potentials of the grids to which it is coupled by an amount four times that of the tending of bus I33, and finally when the last carry-over tube 14 is turned on (bus I41) it tends to produce a potential change eight times as great. The variations due to buses I4I, I40 and I39 tend to oppose those of bus I33; Couplings to bus I34 establishes only constant biases in addition to these variations.

The manner of operation can be followed by considering what happens to the grid of the indicator tube I2I when the tubes 36 of the driving row become conducting one by one. When no tubes are on, bus I33 is at its most positive potential, almost volts, and the bias of the grid of the indicator tube I2I is adjusted so that it is just at zero, and the indicator tube is conducting, a state corresponding to the digit 0. When one intensity tube 36 becomes conducting, the bus I33 becomes more negative, the other buses do not change their potential, and the indicator tube I2I is cut off, a state corresponding to the digit 1. When two tubes 36 are turned on, the amplifying tube I20, which was conducting when there were no or one intensity tube 36 conducting is now cut off by virtue of it proper initial bias. Therefore bus I39 tends to produce a variation of two voltage steps in the grid of the indicator which just compensate the two steps by which the bus I33 has varied, and therefore the indicator tube I2I is brought back to its previous condition and conducts again. For three intensity tubes 36 conducting, the tube I2Iis cut off again,

since only the bus I33 has varied in potential.

For four tubes 36 conducting the amplifying, tube H9 is cut of! by virtue of its original bias, which causes bus I4I toturn on the indicator of the next highest digital place bvcompensating exacting the driving potential .which reestablishes the previous status, and to turn on the indicator for which the previous status is also reestablished since bus I39 came back to its original potential. It may be seen that the indicator I2I and the amplifying tubes operate similarly for more steps as pointed out above.

The anodeszof.theamplifyingtubes H8, H9

A sistances were used, as there conducts. the tubes I52 to I54 are excited so as to S in the binary system. The operating merely the sum of the plate currents of the Since this current is used to excite eight control tubes I44 to I5I in such a wav tube excites the proper carry over 7 over tubes I4, 13 and 12 by a voltage divider (resistance I42 of 1,800,0009 and I43 of 3,300,3009) providing the suitable D.-C. bias. When the .ampliiyin'g tubes are cutofljthe grids of the carryover tubes 14, 13 and I2 must reach zero potential. In order that this be obtained independently of the" accuracy of the coupling resistances I42 and I43, this grid is connected to a diode which is .a part of the amplifying tubes I I8, I I9 and I20. Thus the current through tube I3 depends on the potential of its grid. That potential would be determined only by the ratio of resistances I42 and I43 in the absence of the diodes. Therefore these resistances would have to be very accurate. This requirement is avoided by the diode. When the plate of tube I I9 goes positive (1. e. when the tube is cut-01f) it tends to bring the plate of the diode to an appreciable positive potential. However, this effect is compensated by the current through the diode which flows through resistance I42 and plate resistance of tube II9. This current causes a potential drop through resistance I42 so that the potential of the plate of the diode remains only a few volts positive with respect to its cathode, and assumes thus a "standard potential independent of the accuracy of the resistances I42 and I43. The complete multiplier is composed of a series of 11 circuits as illustrated on Fig. 1, only simpler in that the number S of driving tubes 36 corresponding to the number M of amplifier tubes is smaller. The output carry-over tubes or one circuit are the input carry-overs of the next, as explained above.

The operation of this type of multiplier was found satisfactory for the case tested of P=5 (maximum product 63 63=3969). It is apparent that it depends on the accuracy of the various coupling and cathode resistances since it depends on intensity effects. The resistances should be held within :1 percent. Selected carbon reis no need for wirewound precision resistances. ages must be kept constant within 1 volt, a condition which is easily obtainable with. normal regulation. Dynamic tests, to determine how fast the device can perform a multiplication,

were made by applying a square wave of variable frequency to the input and examining the output voltage in an oscillograph. It was found that the stationary state of the output voltages is reached in about 2 10* seconds. However, in the device tested no precautions of any sort were The supply' volt- 1 intersections interconnected taken to minimize the efiects of tube and lead capacities nor to use sufiiciently low coupling resistances. It is estimated that without increasing the driving power, the time of operation could be 1 reduced by a factor of 10.

Fig. 3 illustrates a second modification wherein an auxiliary row of tubes I44 to I 5| is usedto determine how many of the matrix tubes 36 and carry over tubes 69 and I0 same digital positions are conducting. If such S tubes are conducting, then the El auxiliary tube From the auxiliary tubes I44 to I5I, express current is matrix tubes 36 and carry-over tubes 69 and 0. one of the that the S tube will be excited if there are S conducting tubes in the row, the excited control and indicator tubes because the connections from it to these tubes are made or omitted'depending on whether corresponding to the the digit expressing S in the scale or 2 is one or zero. 1

The circuit of Fig. 3 is based on a push-pull action. The intensityelements 36. 89 and I0, both in the matrix and carry-overs, produce push-pull signals, that is, one signal increasing and one decreasing for every cited tubes. This is obtained by using two triodes for each element (the two triodes of a SSN'IGT) connecting the cathodes together", using a large amount of cathode degeneration to standardize the signals, shifting the currentfrom one tube to: another by maintaining one set of grids I55 at a constant potential and varying the potential of the others I56 (either from the matrix or the preceding carry-over signals) and deriving the pushpull signal from the anodes connected together to form two sets. The push-pull signals are applied to the two control grids of the row of pentagrid converter tubes I44 to I5I (6L7) by means of voltage dividers I51 to I65 and I51 to I65. These voltage dividers are so calculated that the potential of one control-grid '(at least) in any one tube is always negative, except in one tube where both grids are at zero. This causes all the control tubes to be cut ofl except one. As the push-pull signals vary by one step, the tube which was conducting is now cut off because the grid which was at zero potential becomes negative (although the other grid becomes more positive) and the next control tube becomes conducting because the potential of the gridwhich was negative increases just enough to reach zero (although the grid which was positive becomes less positive). The plates of the control tubes are connected to the grids of the carry-over and indicator tubes I52 to I54 and I66 by means of a system of resistances, the connection being made or omitted depending on the control tube, as explained above.

The circuit of Fig. 3 has utility for purposes other than a multiplier of binary numbers. Suppose, for example, that a voltage V varies continuously and that it is desired to indicate on a series of indicators when such voltage passes through definite values V1, V2 Vm. This result is readily achieved by circuit of Fig. 3.

The characteristic features of. the invention are an orthogonal network of conductors having its through tubes which pass current only when bothconductors of the intersection are excited, additional carry-over" tubes connected along additional diagonal leads of the network, indicating means connected to diagonal leads of the network for indicating when an odd number of tubes of the network and of additional carry over tubes on that diagonal are conducting and means for exciting the carry over tubes of one diagonal (corresponding to a given digital binary position) by signals derived from other diagonals (corresponding to lower digital binary positions) when the number of pairs of excited tubes is odd (for the next lowest position), or the number of groups of four excited tubes (for the second lowest position) is odd or when the number of groups of eight excited tubes is odd for the third lowest position, etc. While the'network has been described and illustrated as having anorthogonal arrangement, it is apparent that the two sets of conductors may have other suitable arrangements with respect to one another, the orthogonal arrangement being adapted merely for invention.

change in the number of ex- I claim as my invention:

1. The combination of a plurality of conductors arranged in different sets and each provided with an input lead, output leads, a plurality of resistors each connecting a conductor of one set to a conductor of another set so that each conductor of each set is connected to the conductors of the other set, a plurality of electron discharge elements each provided with a control electrode responsive to the potential drop of a different one of said resistors and each arranged to deliver one unit of current only when both ends of such resistor are at a predetermined potential, connections between said elements for supplying to successive output leads current units which total from one to a predetermined maximum and decrease from said maximum to one, and means connected between said output leads for making available at the terminals of said output leads potentials representative of the product of a number represented by potentials applied to the input leads of one of said sets and a number represented by potentials applied to the input leads of the other of said sets.

2. The combination of two sets of conductors arranged at one end to'correspond respectively to the successive digital positions of different numbers a permanent conductive connection between each conductor of one of said sets and the conductors of the other of said sets, separate output leads each connected to an intermediate terminal of a different one of said connections for delivering currents which total from one to a predetermined maximum and from said maximum to a predetermined minimum, and means for adding to the current of certain of said output leads one current unit when the total number of units of current of a next lower digital position conductor includes a maximum number of pairs which is odd and another current unit when the total number of current units of a second lower digital position conductor includes a maximum number of groups of four which is odd.

3. The combination of two sets of conductors arranged at one end to correspond respectively to the successive digital positions of different numbers a permanent conductive connection between each conductor of one of said sets and the conductors of the other of said sets, separate output leads each connected to an intermediate terminal of a different one of said connections for delivering currents which total from one to a predetermined maximum and from said maximum to a predetermined minimum, and means for adding to the current of certain of said output leads units of current when the number of units of current in other lower digital position output leads is greater than two. I

4. A binary number multiplier including an orthoganol network having two groups of conductors, means for applyin potentials representative of a multiplicand to the terminals of one of sai groups and potentials representative of a multipier to the terminals of the other of said groups, means forming a permanent conductive connection between said groups at each intersection of said conductors, means for conducting current only when potentials representative of the digit 1 are applied to the conductors of an intersection, means for summating the currents of said conductive means along diagonals of said network, and means for deriving from said summations the product of said numbers.

5. The combination of a network including 10 ovided with input terminals and conductors p 0 groups angularly disposed with arranged in t respect to one another, means forming a permanent conductive connection between said groups at each intersection of said conductors means connected to said permanent conductive means for conducting current only when a predetermined potential is applied to each conductor of an intersection, and means for summating said current along diagonals of said network.

6. The combination of a network including conductors provided with input terminals and arranged in two groups angularly disposed with respect to one another, resistors connected between said groups at each intersection of said conductors and provided with an intermediate terminal, a plurality of electron discharge tubes each provided with a control grid connected to a different one of said terminals, and means connecting in parallel the tubes having their grids connected along the diagonals of said network.

7. The combination of two sets of conductors arranged at one end to correspond respectively.

to successive digital positions of different'num-H bers, a pluralit of output terminals arranged to correspond to successive digital positions of the product of said numbers, means connecting the other end of each of said conductors to a different one of said output terminals, a plurality of electron discharge elements each having a control electrode resistively connected between a different conductor of one of said sets and a different conductor of the other of said sets and each arranged to deliver to a different one of said connecting means one unit of current only when its control electrode is at a predetermined potential, and carry over means for adding current units to the current of said connecting mean n response to predetermined values of current connecting means of lower digital position. v

8. The combination oi! a pair of terminals adapted to be charged to different potentials, three resistance elements connected in series between said terminals, one electron discharge element having an output electrode connected to one of said terminals through one of said resistance elements and to the other of said terminals through the other two of said resistance elements, another electron discharge element having a control electrode connected to the junction between said two resistance elements, and a rectifier responsive to the potential drop of said first anode for stabilizing the potential of said control electrode at a value between those of said terminals.

9. The combination of a plurality of conductors arranged in different sets one of which has a separate input terminal for each digital position of one number and the other of which has a separate input terminal for each digital position of another number, permanent conductive connections between the conductors of said sets, output leads each connected to a diflerent one of said connections, and means connected to said output leads for making available potentials representative of a number which is the product of one number represented by potentials applied to the input terminals of one of said sets and another number represented by potentials applied to the input terminals of the other of said sets.

10. The combination of two sets of conductors arranged at one end to correspondrespectively to the successive digital positions of different numbers, permanent conductive connections between each conductor of one of said sets and all the conductors of the other or said sets, a different said changed control potential is ductors oi minal connected each connected to a output terminal connected toeach of said permanent conductive connection means, means including a plurality of devices each adapted to deliver one unit of current in response to a predetermined potential, means connecting each of said devices to a different one or a predetermined group oi said output terminals, a load device, means responsive to one or said units i'or applying a control potential to said load device and to two or said units for changing said control potential, a carry over device, and means responsi've only tosaid two units for carry over device to deliver a current whereby I neutralized.

11. The combination of a plurality of conductors arranged in sets each provided withinput terminals, permanent conductive connections between each s the other set, a diflerent output terto each of said permanent conductive connections,

responseto a predetermined potential at the one or said output terminals to which it is connected. 12. The combination 01' a. plurality of coni ductors arranged terminals, permanent conductive connections between each conductor oi one set and all the'conductors oi the other set, a diiierent output terminal connected to each of said permanent conductive connections, a plurality of devices each connected to a minals for delivering one unit of current in re- }sponse to a predetermined potential at the one of said'output terminals to which it is connected,

difl'erent one of said output terand means operable in response to said units for makingavailable potentials representative of the product or a number represented by potentials applied to the input leads of one of said sets and a number represented by potentials applied to the input leads oi the other oi said sets.

13. The combination oi a plurality of conductors arranged in sets eachhaving input terminals. resistors connected between each conductor applied to the input leads or one of said sets and a number represented by potentials applied to the input leads of the other or said sets.

15. In a system adapted to be operated by a potentialwhich changes by discrete units, the combination of first, second and third electron discharge elements, a resistance network which is responsive to a predetermined potential for biasins said first and second elements to a current operating said conductor of one set and all the conlead to which it is conand a plurality of devices diflerent one oi said output a 5 terminals for delivering one unit 01 current in in sets each provided with input I is responsive to one oi said first of said elements to a and is responsive to two the second of said eleconductlve condition, units for biasing the non-conductive condition 01' said units for biasing ments to a non-conductive condition, means responsive to the non-conductive condition or said second element for biasing said third element'to a current conductive condition, and means responsive to the current conductive condition of said third element for changing said first element from a non-conductive to a conductive condition.

16. In a system adapted to be operated bra potential which changes by discrete units, the

or a carry entry device, first and secdevices, a resistance network which is responsive to a predetermined potential for energizing said control devices, predetermined number of said ing said first second control electron discharge elements, a conductive network which is responsive to a predetermined potential for biasing said control elements to a current conductive condition, is responsive to a predetermined number 01' said units for and is responsive to twice said predetermined number or units for biasing said second control element to a non-conductive condition, means responsive to the non-conductive condition of said second control element for biasing said carry entry 1 element to a current conducting condition, and

to the current conducting conentry element for restoring element to a current conductive condition.

, 18. In a system adapted to be operated in re- 1 sponse to a potential which changes by discrete units, the combination or carry entry means, a control electron discharge element, resistance means which are responsive to a predetermined potential for establishing current conduction element and responsive to entry means.

' JAN A. RAJCHMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,318,591 Couflignal May 11, 1943 2,404,250 Rajchman a July 16, 1946 FOREIGN PATENTS Number Country Date 410,129 Great Britain May 9, 1934 biasing the first of said control elements to a non-conductive condition. 

